1. Technical Field
This invention relates to the field of designing closure apparatus for overhead sliding doors and, more particularly, to a hydraulic door opening or closing device.
2. Description of the Prior Art
In the early part of the twentieth century, elevator door closures were recognized to be too abrupt and too prone to cause accidents to cargo or passengers. Consequently, door closers and check devices involving liquid-filled cylinders or, alternatively, pneumatic enclosures for spring-loaded devices were developed to rectify the abrupt closure and safety problems.
Typical of this early art is U.S. Pat. No. 1,712,089 which issued May 7, 1929 for an Elevator Door Actuating Mechanism. There is shown in FIG. 7 a horizontal operating cylinder pressing against a spring. Fluid is supplied to the cylinder through a valve such that the cylinder opens and closes an elevator gate. Further, a dash pot is suggested to retard the downward movement of the valve as the gate is completely closed.
Eventually it was discovered that a hydraulic fluid-filled cylinder could be sequentially emptied and filled so as to drive a door opening and closure. For example, in U.S. Pat. No. 1,754,563, a valved cylinder drives a piston by fluid pressure and a dash pot retards the final closing of the door.
Today, power elevator car and hoistway doors typically utilize AC motors and various linkages of such motors with gear boxes, checks, pulleys, and so on to provide motion for power door operation. Generally, power door openers using single speed AC motors provide a constant opening and closing speed checked and slowed by air or oil checks. The air and oil check speed control arrangements must be particularly adjusted and often require supplemental control arrangements. Furthermore, AC motor systems are complicated to construct and comprise a large number parts. Many of these parts are susceptible to wear and require frequent maintenance.
With the advent of synchronous DC motors as applied to the opening and closure of elevator sliding doors, the early work in the field of hydraulics and pneumatics was not further advanced. The application of such DC motors for door opening and closure, however, advanced the degree of door control, in particular, the ability to change door opening and closing speeds and to provide a responsiveness to external stimulae, such as electric eye detection of entry and egress, control panel button selection, or control signals from a central elevator or elevator bank control system. In order to accomplish this new control and responsiveness, the complexity of such DC motor arrangements is substantially increased, especially the amount of switching and motor control hardware required. Speed control is especially complicated by the typical provision of special control systems for adjusting the speed output of the DC motors and, thus, the door opening and closing speeds.
In light of the above, it has become desirable to provide a speed-controlled door opening device that is as efficient as the known DC motor controlled arrangements, but which greatly reduces the amount of hardware required and, especially, the number of individual piece parts, and which can be factory-adjusted before shipment to the customer, reducing the installation time.